
where \(\Pi _h\)  denotes the \(L^2(\mathcal {E}_h)\) -projection onto the tangential
facet finite element space \(\widehat{\hbox{$V$}}_h^{k-1}\) .
Efficient implementation of this local projector \(\Pi _h\)  was discussed in
[1]}.
Here \(\alpha >0\)  is a sufficiently large stabilization parameter that
ensures the following coercivity result:
\(A_h^{i}((\hbox{$v$}_h, \widehat{\hbox{$v$}}_h),(\hbox{$v$}_h, \widehat{\hbox{$v$}}_h))\ge \frac{1}{2}\sum _{K\in \mathcal {T}_h^i}\left(\Vert \hbox{$D$}(\hbox{$v$}_h)\Vert _K^2+\frac{\alpha k^2}{h}\Vert \Pi _h(\mathsf {tang}(\hbox{$v$}_h-\widehat{\hbox{$v$}}_h))\Vert _{\partial K}^2\right),\) 
